The present invention is directed to a UHF-feedback oscillator for a frequency range of at least 300 MHz to 1000 MHz with an amplifier stage, a voltage controlled tuning filter and a feedback quadripole.
Oscillators of the above-mentioned type consist of an amplifier stage with amplification factor v and phase shift .phi..sub.v, a voltage controlled tuning filter with damping k and phase cycle .phi..sub.N, and a phase shifter with amplitude cycle m and phase shift .phi..sub.S arranged in a feedback path. In order that such a circuit arrangement functions as an oscillator, the voltage fed back to the oscillator input must coincide in value and in phase with the input voltage, or it must satisfy the following condition: EQU v.k.m.=1.phi..sub.V +.phi..sub.N +.phi..sub.S =n..pi.(n=0, 2, 4 etc.)
A feedback oscillator equipped with a feedback quadripole is known from German Patent Application DE-OS No. 33 05 453. The oscillator of this reference comprises a surface wave transmission line with a path range or transmission band corresponding to a predetermined oscillator frequency, and a 3 dB-90.degree. coupler in the feedback path. The particular utilization of such an oscillator occurs in the transmission of digital signals with transmission velocities exceeding 100 Mbit/s.
Based on the given circuit structure, this oscillator generates a rectangular cycle signal up to a frequency of a maximum of 500 MHz where the possible frequency tuning range lies within .+-.100 KHz. The space requirement for this oscillator depends on the size of the surface wave transmission line (SAW-quadripole) which has a surface of several cm.sup.2. In addition, the cost for such an oscillator is very high because SAW-quadripoles are expensive.
Another type of feedback oscillator is described in German Patent Application No. DE-AS 22 45 476. This oscillator is also intended for use as a timing or clock pulse oscillator in data processing installations. The working frequency of this oscillator can be up to 100 MHz. Band pass filters are utilized for positive feedback within the oscillator which are built up from logic building blocks. The oscillator frequency is determined either by LC (inductance, capacitance) circuits or by means of a crystal.
The best known and most used method for generating oscillations of the highest frequency in the frequency range above 300 MHz is achieved with a Colpitt circuit arrangement, where a fed back LC oscillation circuit is utilized as the frequency determining part. Frequency tuning is achieved by changing the inductance or capacitance. But reactances are changed at the same time if operating frequencies around 900 MHz are required. The quality of such an oscillator is usually relatively high, but the variable frequency range is very narrow and lies at approximately .+-.35%. The geometric structure of this oscillator requires a large space because of the inherent size of the individual electronic components. The Colpitt oscillator design is described in the German text, Pocketbook of High Frequency Technology (Taschenbuch der Hochfrequenztechnik), by H. Meinke and F. W. Gundlach, Springer Edition, 1956 on pages 1318 and 1319.
A special disadvantage of known UHF-feedback oscillators is that variable frequency tuning is only possible within a comparatively narrow frequency range and miniaturization cannot be performed in view of the size of the components.
For the UHF range of approximately 4 to 22 GHz, an oscillator with a gyromagnetic resonator is known from U.S. Pat. No. 4,630,002. Such a resonator is based on the magnetic moment arising from the intrinsic rotation of electrons, wherein the interrelationship between matter and the electromagnetic field can occur only in those frequency ranges whose energy is sufficiently strong for this purpose. Such frequency ranges lie in the gigahertz range.